I don't know what the actual L/D values are, but they should be different between different models because you've got different finess ratios on the fuselages and different wing loadings (same planform, different weights). Winglets and not-winglets will also make a difference.

Has to be, I think. Higher wing loading forces you to higher Cl at a given speed, which means lower L/D for that speed. Since this applies to all speeds, the whole L/D vs. speed curve moves down with increasing wing loading, so it can't have the same L/D max.

Good point. I started realizing I'd done something funny after I posted...I think I was subconsciously imposing an equal payload constraint. With equal payloads, the gross weight between two derivatives is necessarily higher and the heavier one will always have lower L/D max *for that payload*. But if we're just talking max theoretically possible at any weight/speed then you're absolutely right, wing loading shouldn't play into it.